1. Field of the Invention
The present invention relates to cementitious compositions comprising Portland cement, coal combustion byproducts, expanded or extruded polystyrene, and, optionally, fiber. The invention further embraces lightweight structural units such as concrete masonry units (hereinafter "CMUs") produced from the cementitious composition of the present invention and a block machine used for preparing CMUs from the cementitious composition. The CMUs are used in the mining and construction industries.
2. Description of the Prior Art
It is well known in the mining industry to use CMUs to seal off areas in an underground mine which are not in use, and to direct the flow of air in areas which are in use, for the purpose of controlling ventilation in the mine. It is also well known to use structural units, such as CMUs, in the construction industry for the fabrication of masonry structures and the like.
Cementitious compositions used in the past to produce CMUs include combinations of Portland cement; coal combustion byproducts; sand, limestone and other aggregates; and water. These CMUs typically have a density ranging from 75 to 130 pounds per cubic foot, and have dimensions of approximately 8".times.8".times.16".
CMUs manufactured from these compositions are traditionally manufactured using one of two processes, typically depending on the water content of the mixture: (1) the block machine process, when the water content of the mixture is low (a mixture with low water content, i.e. from 0.01 to 5 gallons of water per cubic foot of dry mixture, is typically referred to as having a "low slump"), and (2) the "wet-pour" process, when the water content of the mixture is high (a mixture with high water content, i.e. from 5 to 10 gallons of water per cubic foot of dry mixture, is typically referred to as having a "high slump"). The manufacturing process utilizing the block machine, such as a Besser Block Machine, Model No. V312, includes feeding the cementitious composition into a mold, applying pressure and vibration while the composition is in the mold, extracting the resulting product from the mold and kilning and/or drying the product. Certain traditional CMUs must be manufactured using the "wet-pour" process due to the high slump of the cementitious composition used in the manufacture of such CMUs. The "wet-pour" process includes pouring the cementitious composition into a mold and, while still in the mold, kilning and/or drying the product. This latter process is more time consuming than the block machine process and requires the use of a number of molds during the manufacturing process. While a block machine requires an extensive start-up cost, ultimately the block machine process is less expensive and more efficient than the "wet-pour" process.
The CMUs produced from the traditional cementitious compositions described above are heavier than preferred for use in the mining industry. Preferably, the CMUs used in the mining industry are ultra-lightweight, i.e., having a density of from 25 to 45 pounds per cubic foot, and dimensions ranging in size from 6".times.16".times.24" to 8".times.16".times.24". A cementitious composition used in the past to produce such ultra-lightweight CMUs comprises Portland cement, coal combustion byproducts, soap bubbles and water. Due to the introduction of soap bubbles into the composition, the composition necessarily has a high water content, and therefore a high slump, to incorporate and maintain the soap bubbles. As a result, these ultra-lightweight CMUs must be manufactured using the "wet-pour" process described above, and therefore the resulting CMUs must dry for an extended period of time while still in the molds, which is more expensive and more time consuming than is the use of the block machine.
The ultra-lightweight CMUs produced from a cementitious composition comprising soap bubbles also tend, when subjected to certain environmental conditions (such as low humidity, vibration, foam density, and high heat), to lose their shape and to vary in sine and density. Furthermore, the prior art ultra-lightweight CMUs tend to break and crack during their manufacture, shipment and/or installation.
Accordingly, there is a need in the art for a cementitious composition which can be used in a block machine for the manufacture of large and ultra-lightweight CMUs, which will maintain their shape (and thus size and density) and which are easily toolable with standard masonry tools, and which will not break or crack during their manufacture, shipment and/or installation.
Typically, a conventional block machine, e.g., the Besser Block Machine, Model No. V312, is used to manufacture CMUs using a cementitious composition. Block machines are well-known in the relevant arts and are commercially available. Furthermore, a conventional block machine comprises a number of well-known components working together in forming a CMU. Conventional block machines and their components are well known to persons of ordinary skill in the relevant arts. The different components of a conventional block machine and their function during the manufacturing process are as follows:
(1) A feed box drawer having a strike-off bar at one end is positioned over a mold box and receives a predetermined amount of a cementitious composition; PA1 (2) Upon receiving the predetermined amount of cementitious composition, the feed box drawer traverses a pair of rails and passes over the mold box. As it passes over the mold box, the feed box drawer fills the mold box with the cementitious composition; PA1 (3) Once the feed box drawer fills the mold box with the cementitious composition, the feed box drawer retracts along the rails such that the strike-off bar passes over the top of the mold box and levels, or screeds, the cementitious mixture in the mold box and removes any excess cementitious composition; PA1 (4) After the feed box drawer has retracted, the stripper head lowers and cementitious composition in the mold box is compacted by means of vibration and pressure into a CMU; and PA1 (5) After the CMU is formed, the CMU is removed from the mold box on a production pallet. PA1 These components of a conventional block machine and the operation thereof are described in several prior patents. For example, in U.S. Pat. Nos. 5,059,110 and 5,219,591 to Allison, et al. (collectively, the '591 Patent), an apparatus for forming concrete blocks is described having a feed drawer positioned over a mold box and having a strike-off plate, and tracks on which the feed drawer traverses when filling the mold box with a concrete material. These components operate in the conventional manner as described above. See '591 Patent, Col. 5, Lines 25-33, Lines 55-59; and Col 7, Lines 31-61.
In addition, other prior patents, dating as early as 1918, disclose these well-known principals of block machines. In U.S. Pat. No. 1,268,226 to Flood on Jun. 4, 1918 (the '226 Patent), a brick press is disclosed having a strike-off bar (See '226 Patent, Pg. 2, Lines 30-37), a feed drawer positioned over a mold box (See '226 Patent, Pg. 2, Lines 21-30, Lines 42-45), and tracks, called connecting rods, on which the feed drawer traverses over the mold box (See '226 Patent, Pg., Lines 21-23). These components are also illustrated on the figures. See '226 Patent, FIGS. 1, 4-6.
In U.S. Pat. No. 4,369,153 to Nash, et al. on Jan. 18, 1983 (the '153 Patent), a machine for casting concrete members is disclosed that also describes the general and well-known components of a conventional block machine. In particular, the disclosed machine incorporates a screed, or strike-off, plate for smoothing the surface of the concrete in an extruder or mold (See '153 Patent, Col. 7, Lines 47-50; Col. 8, Lines 1-6), a vertical alignment of a bin, or feeding drawer, over a mold (See '153 Patent, Col 4, Lines 29-36; Col. 6, Lines 22-26, Lines 59-63), and the use of rails (See '153 Patent, Col. 5, Lines 15-17). See also '153 Patent, FIGS. 1a-4.